Intro: Bending Large Aluminium Sheet Without a Brake / Building a Car Roof Storage Pod / Box
We have a camper trailer that I mounted a roof pod on that I found on the side of the road in a verge side collection/“bring out your dead”. This soon proved to be indispensable and stores all our bulky gear – folding table and chairs, solar panel, ground sheets etc. This has degraded over time (cracks, hinge broken) and needed replacing.
Due to the size of stuff stored, I was limited on what size box I could get as a replacement – it had to fit the table (930 x 750 mm) and the solar panel (1200 x 700mm) – so that set the minimum width and length. Existing box was about 400 deep.
I looked around and new I was looking at $1200+, and $500 for a second hand one. So I thought about building my own.
Weight was as an issue, so I thought of aluminium. I could get a 2.4m x 1.2m aluminium sheet for $90. So if I fold it up, and the sides are 200mm deep, that would make it 800mm wide – perfect. And 200 mm deep ends would make it 2m long – also perfect. So two sheets should make a box around 2000 long, 800 wide and 400 deep.
The question was, could I make 2m long folds in the aluminium? I did some research and have previously made small things with 1.6mm thick aluminium – so I thought I would risk it and give it a go.
Step 1: Plan, Design, Work Out What You Need
My plans were pretty simple. I thought about drawing them up properly to post here but figured my “working drawings” give a much better idea of the level of detail that I planned/designed to!!
Plan was to fold and rivet as I don’t have an aluminium welder and did not want to build a frame and rivet sides to it. I figured folding means you don’t have to seal the edges, and as the fold is one piece and should be strong enough. Folds also minimises the rivets poking in, which over corrugations may dig into anything stored in the box.
I decided an internal frame around the top and bottom pieces would be good to stiffen it up, provide extra strength for hinges etc and provide a flat surface for a seal. Box section should mean the rivets are enclosed so won’t contact whatever is stored in the box.
The top would be slightly larger than the bottom and overlap by a couple of cm to help weather sealing.
My build order was:
- Route, cut and fold the bottom piece
- Build the frame to go inside the bottom piece based on as-folded dimensions (luckily same as planned)
- Build top frame to match bottom frame (see sketch – inside dimension of top frame is same as bottom frame
- Based on the outside dimensions of the top frame, work out top frame cuts/folds
- Make top, fit frame then add hinges etc
Step 2: Materials and Tools
Materials (Australian $):
- 2 off 2.4 m x 1.2m x 1.6mm aluminium checker/tread plate - $90 each
- 2 off 25mm x 25mm x 3mm wall x 3m long aluminium SHS - $25 each
- 2 off 35mm x 15mm x 1,5mm wall x 3m long aluminium RHS - $17 each
- Aluminium delivery - $66
(Total for aluminium - $330)
- Box of 1000 rivets – 4.8mm x 6.4mm - $20 – used around 300
- 3 off hinges - $ 5 each
- 2 off latches - $16 each
- 2 off Gas struts 535mm 200 N (20 kg) -$16.50 each
- Tube of Silicon glue/sealant $16
- Bolts, nuts and washers for hinges and latches (had in stock – say $20)
- Rubber sealing strip - $7
- Rubber edging - $5 from ebay
(total other - $148)
TOTAL MATERIALS - $478
- Table to work on (and enough space to work around!)
- Angle iron to put along edge of table to help bend
- DIY bending assistant (in my case two bits of angle and vice grips)
- Router and V bit
- Rubber mallet and hammer
- Clamps etc
- Cordless drill and drill bits
- Rivet gun
- Safety gear – ear protectors, safety glasses, gloves
Warning – the edges of the aluminium can be very sharp, particularly after it has been cut. File edges off and use gloves as required.
Step 3: Marking, Grooving and Cutting
I laid the sheet out on my table and measured it out and marked it with a felt marker. I allowed +3mm on the tabs that are to be folded as they overlap the sheet they fold over – hopefully the photos make more sense.
I then used a V bit in my router to make a 0.1 – 0.2 mm groove where I wanted to the folds to be to help encourage the aluminium fold in the right spot. These groves wound up pretty rough, but I think they helped.
At the “nodes” of cuts and folds I drilled a 6mm hole. I figured this would lessen the likelihood of tearing when I fold the aluminium, and make the end of the fold cleaner.
I then made the cut where appropriate with a jigsaw and fine blade.
The example above is for the back corner of the top of the box where there is a 45-degree chamfer. Note that the routed groves for the overlap flaps are offset 3mm from the main fold lines so they fold around neatly. Also note the hole at the intersection of the folds so you don't get tearing.
Step 4: Somewhere to Work
This is the table I used to fold the aluminium on – it is around 700 x 1300mm. I placed a 25 x 25 angle along the bending edge to give a sharp edge to bend over and lessen the damage to the table when I pounded on the aluminium with the rubber hammer.
I made a "tool" from vice grips and a couple pieces of angle to get extra leverage and to help getting the bends.
Step 5: Folding
By lining the routed grove up with the angle along the table edge and the end of the "tool", you can focus the bend where you want it. Move slowly along the fold, doing 10 – 20 degree bends at a time. Also, after each bending pass, work along with rubber mallet to sharpen the bend by bashing either side of the bend on the table edge.
Once it is bent to around 45 degrees, move to floor where you can stand on the aluminium while you bend it - gives you more leverage and a tighter bend.
Step 6: Ends
After doing the two sides, put it back on the table to do the ends (again with a piece of angle on the table edge). The drop sheet in the photo is there to help keep the noise down when hammering with the rubber mallet so I don’t disturb the neighbours too much. Hearing protection is important when bashing!
This is the end product of the forming phase before inserting the frame and riveting
Here I am checking the overlap folds before riveting etc
Step 7: Add the Frame
Here it is with the internal frame installed. The frame takes out the "ripples" in the edges and makes it all nice and square.
Photo of the finished folded corners all riveted etc. I used an acid based silastic as a glue/sealer.
Step 8: Trial Fit
Here is my trial fit of top and bottom - thankfully all good!
Step 9: Hinges
Due to the offset where the top and bottom overlap, I needed offset hinges. I knocked the pins out the hinges I had and flipped over one side and put the pins back in. Top hinge in the photo below if before, bottom after.
I put nylon between hinges (galvanized) and aluminium to help reduce dissimilar metal corrosion. This isn’t perfect but should do for what we want.
I also used some offcuts to make doubler plates where the hinges are to stiffen up the material a bit.
Step 10: Finishing
Here it is with the hinges, catches and gas struts installed and ready to mount on the camper trailer.
There is a soft rubber strip installed where the top and bottom frames meet to provide a seal. This is installed on the top frame so it is out of the way when the box is open and isn’t damaged by things being dragged across it.
The bottom edge of the top/lid was very sharp, and I was worried if it came down when being used (eg wind blows it down) it could give a nasty cut, so I added on some edging to make it less of a hazard.
Step 11: Mounting
Finished product all mounted and ready to go.
Finished box is 2m long x 800 wide x 380 high and weighs 30 kg all up.
Overall, I’m stoked at how it has worked out – I was taking a shot in the dark here if I would even be able to bend the aluminium in a straight line. It won’t make the centrefold of metalwork monthly, but it worked out way beyond my expectations will be perfect for what we want.